An electron type endoscope (which shall be briefly mentioned as an electronic endoscope or electronic scope) wherein such solid state imaging device as a charge coupled device (abbreviated as CCD) is used instead of an image guide transmitting optical images is recently practiced so that an imaged endoscope picture image may be displayed on a TV monitor.
Also, a photographing camera (which shall be briefly mentioned as a still camera) is fitted to an eyepiece part of an optical endoscope (which shall be briefly mentioned as a fiber scope) wherein a conventional image guide is used so as to take a photograph or a TV camera containing such imaging means as a solid state imaging device is fitted to the same part so as to display a picture image on a TV monitor.
Now, the above mentioned electronic scope or fiber scope is used as connected to a light source apparatus feeding an illuminating light.
Conventionally, such light source apparatus is made in advance to be connected with a fiber scope so that, when a still camera is connected to the fiber scope, an iris will act so that the film surface illuminating degree may be constant and an automatic light adjustment will act. Therefore, even if the observing position varies, by the action of this automatic light adjustment, an object to be observed will be able to be observed by the observer always at a constant brightness. Further, the automatic light adjusting circuit is so designed that the responsiveness will be optimum when a still camera is connected.
However, it is in more cases that a TV camera is connected to a fiber scope and a picture image is observed on a TV monitor. For the light adjustment in such case, a video signal from the TV camera is input as an automatic light adjusting signal into the above mentioned automatic light adjusting circuit. However, this automatic light adjusting circuit corresponds to the still camera as mentioned above, therefore can not he said to be most suitable particularly in the responsiveness, for example, a hatching (the response is too early to be stable and flutters) and response delay (the response is too late to follow the variation of the brightness of the object) have occurred and such disadvantage that the observer is not only fatigued in the eye but also can not make a sufficient diagnosis has occurred. Further, in case an electronic scope is connected to one light source apparatus, the video signal from the electronic scope will be of the same kind as of the TV camera and, when it is connected to the automatic light adjusting circuit for the fiber scope, the same disadvantage as is mentioned above will occur.